1. Field of the Invention
The present invention relates to an optical waveguide for a touch panel, and a touch panel using the same.
2. Description of the Related Art
Touch panels are input devices for operating an apparatus by directly touching a display screen of a liquid crystal display device or the like with a finger, a purpose-built stylus or the like. The touch panels include a display which displays operation details and the like, and a detection means which detects the position (coordinates) of a portion of the display screen of the display touched with the finger or the like. Information indicative of the touch position detected by the detection means is sent in the form of a signal to the apparatus, which in turn performs an operation and the like displayed on the touch position. Examples of the apparatus employing such a touch panel include ATMs in banking facilities, ticket vending machines in stations, portable game machines, and the like.
A detection means employing an optical waveguide is proposed as the detection means for detecting the finger touch position and the like on the above-mentioned touch panel (see, for example, US 2004/0201579A1). Specifically, the touch panel includes optical waveguides provided around a periphery of a display screen of a rectangular display. The touch panel is configured to emit a multiplicity of light beams parallel to the display screen of the display from light-emitting portions of a light-emitting optical waveguide provided on one side portion of the display screen of the display toward the other side portion, and to cause the light beams to enter light-receiving portions of a light-receiving optical waveguide provided on the other side portion. These optical waveguides cause the light beams to travel in a lattice form on the display screen of the display. When a portion of the display screen of the display is touched with a finger in this state, the finger blocks some of the light beams. Therefore, the light-receiving optical waveguide senses a light blocked portion, whereby the position of the above-mentioned portion touched with the finger is detected.
The multiplicity of light beams emitted from the above-mentioned light-emitting optical waveguide are light beams emitted from the light-emitting portions (tips) of a multiplicity of light-emitting cores, respectively, which are arranged along the one side portion of the display screen of the display. As the multiplicity of light-emitting cores, there have been proposed light-emitting cores 53 formed by dividing a tip portion of a single original core into a multiplicity of branches fanned outwardly, as shown in FIG. 8 (see US2006/0188198A1). The branch structure of the original core includes a substantially rectangular widened portion 52, a strip-shaped rear end portion 51 extending from the rear end of this widened portion 52, and the multiplicity of light-emitting cores 53 fanned outwardly from the front end of the above-mentioned widened portion 52 as a branch point. The above-mentioned strip-shaped rear end portion 51 has an optical axis (not shown) extending in the longitudinal direction thereof.
However, the multiplicity of light-emitting cores 53 in the form of the branches fanned outwardly as disclosed in US 2006/0188198A1 described above are disadvantageous in that light beams emitted from the light-emitting portions of light-emitting cores 53A near the center of the fanned-out configuration thereof (light-emitting cores near the extension of the optical axis of the rear end portion 51 of the original core) are of high intensity, and light beams emitted from the light-emitting portions of light-emitting cores 53B near opposite ends of the fanned-out configuration thereof are of lower intensity. When such an optical waveguide is used as the touch position detection means for a touch panel, the finger touch position cannot be detected in some cases in the low-intensity portion.
The present inventor has made studies to diagnose the cause of the nonuniform intensity of the light beams emitted from the light-emitting portions of the above-mentioned light-emitting cores 53 depending on the branch position of the light-emitting cores 53. As a result, the present inventor has found that the above-mentioned problem lies in the shape of the above-mentioned widened portion 52 and in the light beams reflected therefrom.
Specifically, the above-mentioned widened portion 52 is of a substantially rectangular configuration widened leftwardly and rightwardly with respect to the rear end portion 51 of the original core, as shown in FIG. 8. A majority of light beams coming through the rear end portion 51 of the original core into the above-mentioned widened portion 52 travel toward the light-emitting cores 53. Some of the light beams, however, travel toward both left-hand and right-hand side surfaces 52a of the widened portion 52, as indicated by alternate long and short dashed lines shown. The light beams traveling toward the left-hand and right-hand side surfaces 52a reach front side portions 52a, of the left-hand and right-hand side surfaces 52a of the above-mentioned widened portion 52, but scarcely reach rear side portions 52a2 of the left-hand and right-hand side surfaces 52a because the light beams are required to be bent at generally right angles to travel. Thus, the reflection of the light beams from the above-mentioned left-hand and right-hand side surfaces 52a occurs at the front side portions 52a1 of the left-hand and right-hand side surfaces 52a. The light beams reflected from such specific areas reach also a specific area, as indicated by the alternate long and short dashed lines shown. For this reason, the reflected light beams enter specific ones (near the center) of the multiplicity of light-emitting cores 53 in the form of the branches. As a result, both the light beams emitted along the optical axis of the rear end portion 51 of the original core and the reflected light beams enter the light-emitting cores 53A near the center among the multiplicity of light-emitting cores 53 fanned outwardly to result in the higher intensity of light beams in the light-emitting cores 53A than in the other light-emitting cores 53B. Such a phenomenon is considered to result in the nonuniform intensity of the light beams emitted from the light-emitting portions of the multiplicity of light-emitting cores 53 in the form of the branches depending on the branch position of the light-emitting cores 53.